Influence of Boundary-Layer Thickness on Base Pressure and Vortex Shedding Frequency

AIAA Journal ◽  
2001 ◽  
Vol 39 (4) ◽  
pp. 754-756 ◽  
Author(s):  
A. Rowe ◽  
A. L. A. Fry ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Vortex Shedding ◽  
Boundary Layer Thickness ◽  
Base Pressure ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

Boundary Layer Closure and Heat Transfer in Constant Base Pressure and Simple Wave Guns

1978 ◽  
Vol 100 (4) ◽  
pp. 690-696 ◽  
Author(s):  
A. D. Anderson ◽  
T. J. Dahm
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Method Of Characteristics ◽  
Simple Wave ◽  
Momentum Equation ◽  
Base Pressure ◽  
Two Dimensional ◽  
The Method Of Characteristics

Solutions of the two-dimensional, unsteady integral momentum equation are obtained via the method of characteristics for two limiting modes of light gas launcher operation, the “constant base pressure gun” and the “simple wave gun”. Example predictions of boundary layer thickness and heat transfer are presented for a particular 1 in. hydrogen gun operated in each of these modes. Results for the constant base pressure gun are also presented in an approximate, more general form.

Boundary-layer thickness and base pressure

AIAA Journal ◽  
1985 ◽  
Vol 23 (12) ◽  
pp. 1987-1989 ◽  
Author(s):  
Mauri Tanner
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Base Pressure

Vortex-Induced Vibration for Heat Transfer Enhancement

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Enhancement ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Pressure Loss ◽  
Thermal Boundary Layer ◽  
Transfer Enhancement ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

A passive, self-agitating method which takes advantage of vortex-induced vibration (VIV) is presented to disrupt the thermal boundary layer and thereby enhance the convective heat transfer performance of a channel. A flexible cylinder is placed at centerline of a channel. The vortex shedding due to the presence of the cylinder generates a periodic lift force and the consequent vibration of the cylinder. The fluid-structure-interaction (FSI) due to the vibration strengthens the disruption of the thermal boundary layer by reinforcing vortex interaction with the walls, and improves the mixing process. This novel concept is demonstrated by a three-dimensional modeling study in different channels. The fluid dynamics and thermal performance are discussed in terms of the vortex dynamics, disruption of the thermal boundary layer, local and average Nusselt numbers (Nu), and pressure loss. At different conditions (Reynolds numbers, channel geometries, material properties), the channel with the VIV is seen to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% in comparison with a clean channel and a channel with a stationary cylinder, respectively. The cylinder with the natural frequency close to the vortex shedding frequency is proved to have the maximum heat transfer enhancement. When the natural frequency is different from the vortex shedding frequency, the lower natural frequency shows a higher heat transfer rate and lower pressure loss than the larger one.

Flow Around a Normal Plate of Finite Width Immersed in a Turbulent Boundary Layer

1983 ◽  
Vol 105 (1) ◽  
pp. 98-104 ◽  
Author(s):  
H. Sakamoto ◽  
M. Arie
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Turbulent Boundary Layer ◽  
Power Function ◽  
Vortex Shedding ◽  
Stream Velocity ◽  
Finite Width ◽  
Pressure Drag ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

An experimental investigation was carried out on the flow around a normal plate of finite width mounted on a smooth plane wall along which a turbulent boundary layer was fully developed. Experimental data were collected to investigate the effects of (1) the aspect ratio of the plate (2) the parameters characterizing the boundary-layer on the pressure drag and the vortex shedding frequency. The pressure drag coefficient of the plate defined by CDτ = D/(1/2ρuτ2hw) was found to be expressed by a power function of huτ/ν in the range h/δ<1.0 for each aspect ratio w/h, where D is the pressure drag, uτ is the shear velocity, ρ is the density of fluid, h and w are the height and the width of the plate, respectively, ν is the kinematic viscosity, δ is the thickness of the boundary layer. Also, the Strouhal number for the plate defined by St =fc • w/ U0 was found to be expressed by a power function of the aspect ratio w/h in the range of h/δ less than about 1.0, where fc is the vortex shedding frequency, U0 is the free-stream velocity. As the aspect ratio was reduced, the type of vortex shedding behind the plate was found to change from the arch type to the Karman type at the aspect ratio of about 0.8.

An Investigation of the Effects of Incidence on the Flow Around a Square Section Cylinder

1983 ◽  
Vol 34 (4) ◽  
pp. 243-259 ◽  
Author(s):  
E.D. Obasaju
Keyword(s):  
Vortex Shedding ◽  
Pressure Coefficient ◽  
Rate Of Change ◽  
Base Pressure ◽  
Angle Of Incidence ◽  
Spacing Ratio ◽  
Spectral Peaks ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

SummaryA study has been made of the changes that take place in the flow around a square section cylinder as the angle of incidence is increased from 0° to 45°. Measurements of the Strouhal number, S, and the vortex longitudinal spacing, a/d, are presented and used to estimate the vortex strength,, and vortex street spacing ratio, b/a.is found to vary between about 1.2 and 1.7 depending on incidence, and is given approximately by 0.52(1 - Cpb)/2πS, where Cpbis the mean base pressure coefficient. As the incidence is increased from 0°, S at first decreases slightly and then rises sharply to a maximum at 13.5° incidence, which is the incidence where reattachment of the shear layer, in some mean sense, is expected to commence. The spectra of pressure and velocity fluctuations were measured and subharmonic peaks were found in both spectra at 5° and 10° incidence. It is suggested that they may have been caused by an interaction between a vortex and a trailing edge corner. The degree of organisation of the vortex shedding process was estimated by calculating the sharpness factor, Q, of the spectral peaks at the vortex shedding frequency. In general Q fluctuated with changes in incidence. High values of Q occurred at angles of incidence where the rate of change of the mean base pressure coefficient with incidence is very small whereas low values occurred where the flow is changing to a different state.

Sign in / Sign up

Export Citation Format

Share Document